A tamr (Thermal Assisted magnetic recording) write head uses the energy of optical-laser generated plasmons in a plasmon antenna to locally heat a magnetic recording medium and reduce its coercivity and magnetic anisotropy. To enable the tamr head to operate most effectively, the maximum gradient of the magnetic recording field should be concentrated in the small region being heated. Typically this does not occur because the spot being heated by the antenna is offset from the position at which the magnetic pole concentrates its magnetic field. The present invention incorporates a magnetic core within a plasmon antenna, so the antenna effectively becomes an extension of the magnetic pole and produces a magnetic field whose maximum gradient overlaps the region being heated by edge plasmons being generated in a conducting layer surrounding the antenna's magnetic core.
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1. A tamr head comprising:
a magnetic write pole which, when energized, produces a magnetic field for writing on a magnetic recording medium;
a source of electromagnetic radiation in the optical frequency range;
an optical waveguide for directing said electromagnetic radiation to a plasmon antenna, wherein said optical waveguide couples said electromagnetic radiation to a plasmon mode generated within said antenna;
the plasmon antenna for generating and maintaining said plasmon mode within a plasmon generating layer and transferring energy generated by said plasmon mode to a localized region of said magnetic recording medium, thereby heating said localized region and reducing its magnetic coercivity and anisotropy; and wherein
said plasmon antenna includes a magnetic portion for directing said magnetic field onto said localized region, whereby the strength and gradient of said magnetic field within said localized region, combined with the thermal energy profile of said transferred plasmon mode thermal energy creates optimal conditions for writing within said region of reduced magnetic coercivity and anisotropy.
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1. Field of the Invention
This invention relates to the fabrication of magnetic read/write heads that employ TAMR (thermally assisted magnetic recording) to enable writing on magnetic media having high coercivity and high magnetic anisotropy. More particularly, it relates to the use of a plasmon antenna (PA) to transfer the required thermal energy from the read/write head to the media.
2. Description of the Related Art
Magnetic recording at area data densities of between 1 and 10 Tera-bits per in2 (Tbpsi) involves the development of new magnetic recording mediums, new magnetic recording heads and, most importantly, a new magnetic recording scheme that can delay the onset of the so-called “superparamagnetic” effect. This effect is the thermal instability of the extremely small regions on which information must be recorded, in order to achieve the required data densities. A way of circumventing this thermal instability is to use magnetic recording mediums with high magnetic anisotropy and high coercivity that can still be written upon by the increasingly small write heads required for producing the high data density. This way of addressing the problem produces two conflicting requirements: 1. the need for a stronger writing field that is necessitated by the highly anisotropic and coercive magnetic mediums and; 2. the need for a smaller write head of sufficient definition to produce the high areal write densities, which write heads, disadvantageously, produce a smaller field gradient and broader field profile. Satisfying these requirements simultaneously may be a limiting factor in the further development of the present magnetic recording scheme used in state of the art hard-disk-drives (HDD). If that is the case, further increases in recording area density may not be achievable within those schemes. One way of addressing these conflicting requirements is by the use of assisted recording methodologies, notably thermally assisted magnetic recording, or TAMR.
The prior art forms of assisted-recording methodologies being applied to the elimination of the above problem share a common feature: transferring energy into the magnetic recording system through the use of physical methods that are not directly related to the magnetic field produced by the write head. If an assisted recording scheme can produce a medium-property profile to enable low-field writing localized at the write field area, then even a weak write field can produce high data density recording because of the multiplicative effect of the spatial gradients of both the medium property profile and the write field. These prior art assisted-recording methods either involve deep sub-micron localized heating by an optical beam or ultra-high frequency AC magnetic field generation.
The heating effect of TAMR works by raising the temperature of a small region of the magnetic medium to essentially its Curie temperature (TC), at which temperature both its coercivity and anisotropy are significantly reduced and magnetic writing becomes easier to produce within that region. In the following, we will address our attention to a particular implementation of TAMR, namely the transfer of electromagnetic energy to a small, sub-micron sized region of a magnetic medium through interaction with the near field of an edge plasmon excited by an optical frequency laser. The edge plasmon is excited in a small conducting plasmon antenna (PA) approximately 200 nm in width that is incorporated within the read/write head structure. The source of optical excitement can be a laser diode, also contained within the read/write head structure, or a laser source that is external to the read/write head structure, either of which directs its beam at the antenna through a means such as an optical waveguide (WG). As a result of the WG, the optical mode of the incident radiation couples to a plasmon mode in the PA, whereby the optical energy is converted into plasmon energy. This plasmon energy is then focused by the PA onto the medium at which point the heating occurs. When the heated spot on the medium is correctly aligned with the magnetic field produced by the write head pole, TAMR is achieved.
K. Tanaka et al. (US Publ. Pat. App. US2008/0192376) and K. Shimazawa et al. (US Publ. Pat. App. US2008/0198496) both describe TAMR structures that utilize edge plasmon mode coupling.
Rochelle, (U.S. Pat. No. 6,538,617) describes an antenna for sensing magnetic fields that employs a ferrite magnetic core.
Burdick et al. (U.S. Pat. No. 6,424,820) teaches a short wave antenna comprising wire wrapped around a ferrite core.
None of these prior arts address the issues to be dealt with by the present invention.
Referring first to
The conventional magnetic write head includes a main magnetic pole (MP) (1), which is shown with a rectangular ABS shape, a writer coil (5) (three winding cross-sections drawn) for inducing a magnetic field within the pole structure and a return pole (3). Generally, magnetic flux emerges from the main magnetic pole, passes through the magnetic media and returns through the return pole.
The optical waveguide (WG) (4) guides optical frequency electromagnetic radiation (6) towards the air bearing surface (ABS) (10) of the write head. The ABS end of the write head will be denoted its distal end. The plasmon antenna (PA) (2), which has a triangular shape in the ABS plane, extends distally to the ABS. The distal end of the waveguide (4) terminates at a depth, d, away from the ABS. An optical frequency mode (6) of the electromagnetic radiation couples to the edge plasmon mode (7) of the PA (2) and energy from the edge plasmon mode is then transmitted to the media surface where it heats the surface locally at the ABS edge of the PA triangle.
An advantage of the design illustrated in this figure is that the WG (4) terminates before reaching the ABS of the write head so that leakage of visible radiation to the ABS is reduced. Meanwhile, the energy from the edge plasmon mode (7), upon reaching the ABS, can achieve a spatially confined region that is desirable for achieving a high thermal gradient in the magnetic medium. With the long PA body (2) and large volume of metal composing the PA, heating damage of the PA is also greatly reduced.
In the prior art cited above, the materials used to form the PA are metals like Ag and Au that are known to be excellent in generating optically driven plasmon modes. However, in the prior art a problem still exists in aligning the optical heating profile within the region of energy transfer at the medium surface, with the magnetic field profile generated by the write head.
Referring to
As can be seen in
Due to structural limitations, caused, for example, by the thickness and arrangement of the WG and by choice of the PA design, difficulties in alignments during fabrication, etc., optimal alignment of the heating and field profiles cannot be obtained.
It is a first object of the present invention to produce a new TAMR antenna structure in which the simultaneous application of magnetic field and heat to a heating spot on a magnetic medium is optimized to produce a greater effective recording field gradient.
It is a second object of this invention to achieve higher recording density on magnetic recording media by means of the improved TAMR scheme that utilizes the optimal positioning of the magnetic recording field and the thermal energy for heating the medium.
It is a third object of this invention to produce a higher magnetic field at the heating spot in TAMR along with the maximum field gradient.
It is a fourth object of this invention to achieve self-alignment of the magnetic field and thermal power gradients at the heating spot.
It is a fifth object of the present invention to produce an improved plasmon antenna.
It is a sixth object of the present invention to achieve the previous objects without resorting to a significant variation in present fabrication technologies.
These objects will be achieved by means of a plasmon antenna design in which there is a core of magnetic material, such as CoFe or NiFe, overcoated with a non-magnetic highly conductive metal, such as Au or Ag. This proposed antenna composition, with its central magnetic core and with edge plasmon mode excitation resulting from radiative coupling to an optical waveguide substantially confined to the overcoat, will self align the magnetic field gradient with a thermal heating gradient produced by the plasmon mode during magnetic recording. This self-alignment, in which maximum thermal gradients and maximum magnetic field gradients are aligned, will enhance the effective recording field gradient and achieve higher recording density. The fabrication method is easily adaptable to existing head fabrication techniques. By attaching the antenna directly to the writer pole, as in one of the preferred embodiments, the fabrication method can be further simplified and an additional benefit of lower antenna temperature during operation can be achieved.
The objects, features, and advantages of the present invention are understood within the context of the Description of the Preferred Embodiment as set forth below. The Description of the Preferred Embodiment is understood within the context of the accompanying figures, wherein:
The preferred embodiment of this invention is a TAMR write head for producing high density recording on a magnetic medium. The write head incorporates a plasmon antenna of novel structure that is attached to the write head so that a face of the antenna emerges at the ABS of the writer at a position adjacent to the ABS of the main magnetic pole. The plasmon antenna is radiatively coupled to optical frequency electromagnetic radiation generated preferably by an optical laser and guided by an optical waveguide to the plasmon antenna. The radiative coupling generates edge plasmon modes within the antenna whose associated electromagnetic fields impinge on a small surface area of the magnetic medium generating thermal energy with a spatially dependent profile within that area and causing the temperature of that area to increase. The magnetic pole of the writer produces a magnetic writing field, with a spatially dependent field intensity profile that impinges on a surface area that overlaps with the plasmon field. The spatial alignment of the thermal energy distribution and the magnetic field is such that there is substantial overlap at their regions of maximum gradient. This overlap increases the effectiveness of the magnetic field in changing the local magnetization of the magnetic medium so that magnetic writing on the medium is greatly enhanced and can be confined to extremely small surface areas.
Referring to
Referring to
Referring to
During recording, the magnetic field produced by the MP (21) magnetizes the core of the MCA (24) and can even saturate the core if the spacing is small, literally zero spacing being quite appropriate. Thus, the magnetic core of the antenna can be considered a part of the MP structure rather than the MCA structure, in that its role is to direct magnetic flux to the spot on the medium being heated rather than contribute to the heat generating properties of the edge plasmon mode.
Referring to
Referring now to
In addition to the magnetic field advantages produced by the magnetic core antenna of the present invention, there is also a heat sink effect produced by the large metal volume that maintains a low temperature of the antenna. When the medium is heated by the plasmon edge mode at the antenna tip, the antenna itself also heats up. Theoretically, the larger the antenna metal volume, the lower will be the antenna temperature resulting from heating the medium.
Referring to
1. Au/Al2O3: an alumina core partially clad with Au
2. Au/Au: essentially solid Au
3. Au/Au/Au: an Au antenna with an additional layer of Au on the flat side
4. Au/Co/Co: Au cladding, Co core and additional layer of Co on the flat side
5. Au/Co/Au: Au cladding, Co core and additional layer of Au
The additional layers are formed on the face opposite the vertex that supports the edge plasmon mode. Such a layer simulates the additional heat sink effect from a metal backing, for example from a magnetic writer pole as in case 4.
The five maximum temperature values are normalized to percentages of the first configuration. The thermal conductivities have been taken to be 317 W/mK for Au, 2 W/mK for alumina and 93 W/mK for the Co. The core material plays a determining factor in the final maximum temperature of the antenna, with the Au core having the lowest temperature and the alumina core having the highest. The addition a metal layer to the back side of the antenna, opposite to the vertex that supports the plasmon mode, acts as a heat sink (as noted above) and helps to reduce the antenna maximum temperature. Because the magnetic core of the antenna shifts the position of the magnetic writing field, it can be attached directly to the main pole of the write head, thereby using that large metallic element as an additional heat sink. For a prior art antenna with no magnetic core such direct attachment to the main pole may not be as advantageous or beneficial.
Referring to schematic
More specifically, the waveguide (23) transmits an externally generated optical frequency electromagnetic wave into the TAMR head (typically generated by a solid state optical laser mounted externally to the head but adjacent to the head) and couples the optical mode to the plasmon mode in the antenna. The coupling occurs in the encircled region of overlap between the waveguide (23) and the antenna (22). Note it is not the intent of these embodiments to teach the methods by which an optical waveguide or laser is fabricated.
Referring now to schematic
Referring to
The plasmon generating layer (27) can be a layer of material chosen from the group of highly conductive metals, such as Au or Ag, and formed to a thickness of approximately tens of nanometers. The resulting tapered portion of the magnetic pole (24), which comprises a magnetic material used to form a magnetic pole such as single or composites of the following materials Fe, Co, Ni, B, when covered with the metallic, conducting, plasmon generating layer (27) of Au or Ag, together forms the plasmon antenna of the present invention. This layer (27) is preferably between approximately 10 and 100 nm in thickness.
In this and the following embodiments, the combination of magnetic core and metallic overlayer is called the plasmon antenna and it will hereinafter be labeled (22). Note that in this particular embodiment and in the embodiments to follow, the plasmon antenna will be preferably shaped as a triangular prism of substantially isosceles triangular cross-sectional shape. The two sides (or faces) of the prism corresponding to the isosceles legs of the triangle will be covered by the conducting layer as will the vertex of the prism formed by the meeting of these two sides. The base of the prism is substantially free of the conducting overlayer, except where the edges of the overlayer are exposed alongside the edges of the triangular base. The prism is formed longitudinally along the side of the magnetic pole, extending in the direction towards the ABS of the writer.
The tapered edge (i.e., the vertex) of the prism points towards the trailing direction of the TAMR head and directly faces the optical waveguide (23) which is positioned further down-track of the antenna and is separated from the antenna by a space. Preferably the spacing between the vertex of the antenna and the face of the waveguide can be between approximately 0 nm (physical contact) and 100 nm (nm=nanometers=10−9 meters). The length of the plasmon antenna in the direction towards the ABS is between approximately 200 and 5000 nm and the height of the triangular cross-sectional base (base edge to vertex) is between approximately 25 and 500 nm. The width of the base (side opposite the vertex) is between approximately 50 and 1000 nm. Note that these dimensions are characteristic of the plasmon antenna in all embodiments.
The writer pole and the antenna are exposed at the ABS of the TAMR head, while the distal end of the waveguide (i.e., the end closest to the ABS) is recessed by a distance, d, preferably greater than approximately 0.2 microns from the ABS to reduce optical leakage. If light coupling to the antenna is efficient, however, the distal surface of the antenna can be at the ABS. The etched portion of the pole (22) over which the conducting plasmon layer (27) is deposited forms the magnetic core of the antenna, thereby achieving the objects of the present invention. The tapering end of the antenna can be flat (see, for example,
Referring to
As is shown in
Referring to schematic
Referring to
Because of the positioning of the waveguide relative to the antenna, the coupling of the optical mode to the plasmon mode will be through the exposed edges of the metallic layer (27), rather than at the vertex of the metallic layer. To reduce the distance between the write pole (21) and the antenna (22), and to enhance the effects of the magnetic field of the write pole on the magnetic core (24) of the antenna, the writer pole is formed with an “L” shape, as shown in the drawing, with the short leg of the “L” passing beneath the distal end of the waveguide. Because of the unuasual shape of the pole, a method of its formation will be given in the following.
Referring to schematic
Referring to schematic
Referring now to schematic
Referring to schematic
Finally, referring to schematic
Referring to schematic
Referring to schematic
Fabrication of this plasmon antenna configuration can be achieved, for example, in accord with the following steps. Referring to schematic
Referring to schematic
Referring to schematic
Referring to schematic
Referring finally to schematic
Referring to schematic
Referring to schematic
Referring to schematic
Referring to schematic
Referring to schematic
Referring now to schematic
Referring finally to schematic
As is understood by a person skilled in the art, the preferred embodiments of the present invention are illustrative of the present invention rather than being limiting of the present invention. Revisions and modifications may be made to methods, processes, materials, structures, and dimensions through which is formed and used a TAMR write head with a plasmon antenna that provides an optimal overlap of magnetic field gradients and thermal energy transfer gradients on a magnetic recording medium while still providing such a TAMR write head, formed and used in accord with the present invention as defined by the appended claims.
Dovek, Moris, Schreck, Erhard, Zhou, Yuchen, Takano, Kenichi, Jin, Xuhui, Smyth, Joe
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